Cardiac lead placement using multiple spatially distributed sensors

ABSTRACT

A system for facilitating placement of a lead in or on a patient&#39;s heart includes a first lead apparatus, a second lead apparatus, a user interface, and a processor. The processor is configured to measure a distance parameter indicative of a distance between a reference sensor element at a right heart location and a lead apparatus sensor element at each of a plurality of left heart locations in either the left ventricle or a coronary venous pathway, determine a separation distance for each of the plurality of left heart locations from the right heart location based on the distance parameter measurements, and determine that the separation distance for a location of the plurality of left heart locations from the right heart location is less than a threshold distance based on the separation distance for the location. The threshold distance representative of unsuitability for pacing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 12/236,838,filed Sep. 24, 2008, which claims priority to Provisional ApplicationNo. 61/007,595, filed Dec. 13, 2007, all of which are hereinincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to cardiac lead delivery and,more specifically, to cardiac lead placement using a multiplicity ofspatially distributed sensors.

BACKGROUND

When functioning normally, the heart produces rhythmic contractions andis capable of pumping blood throughout the body. The heart hasspecialized conduction pathways in both the atria and the ventriclesthat enable the rapid conduction of excitation impulses (i.e.depolarizations) from the SA node throughout the myocardium. Thesespecialized conduction pathways conduct the depolarizations from the SAnode to the atrial myocardium, to the atrio-ventricular node, and to theventricular myocardium to produce a coordinated contraction of bothatria and both ventricles.

The conduction pathways synchronize the contractions of the musclefibers of each chamber as well as the contraction of each atrium orventricle with the opposite atrium or ventricle. Without thesynchronization afforded by the normally functioning specializedconduction pathways, the heart's pumping efficiency is greatlydiminished. Patients who exhibit pathology of these conduction pathwayscan suffer compromised cardiac output.

Cardiac rhythm management devices have been developed that providepacing stimulation to one or more heart chambers in an attempt toimprove the rhythm and coordination of atrial and/or ventricularcontractions. Cardiac rhythm management devices typically includecircuitry to sense signals from the heart and a pulse generator forproviding electrical stimulation to the heart. Leads extending into thepatient's heart chamber and/or into veins of the heart are coupled toelectrodes that sense the heart's electrical signals and for deliveringstimulation to the heart in accordance with various therapies fortreating cardiac arrhythmias.

Pacemakers are cardiac rhythm management devices that deliver a seriesof low energy pace pulses timed to assist the heart in producing acontractile rhythm that maintains cardiac pumping efficiency. Pacepulses may be intermittent or continuous, depending on the needs of thepatient. There exist a number of categories of pacemaker devices, withvarious modes for sensing and pacing one or more heart chambers.

Pacing therapy has been used in the treatment of heart failure (HF). HFcauses diminished pumping power of the heart, resulting in the inabilityto deliver enough blood to meet the demands of peripheral tissues. HFmay cause weakness, loss of breath, and build up of fluids in the lungsand other body tissues. HF may affect the left heart, right heart orboth sides of the heart. For example, HF may occur when deterioration ofthe muscles of the heart produce an enlargement of the heart and/orreduced contractility. The reduced contractility decreases the cardiacoutput of blood and may result in an increased heart rate. In somecases, HF is caused by unsynchronized contractions of the left and rightheart chambers, denoted atrial or ventricular dysynchrony. Particularlywhen the left or right ventricles are affected, the unsynchronizedcontractions can significantly decrease the pumping efficiency of theheart.

Pacing therapy to promote synchronization of heart chamber contractionsto improve cardiac function is generally referred to as cardiacresynchronization therapy (CRT). Some cardiac pacemakers are capable ofdelivering CRT by pacing multiple heart chambers. Pacing pulses aredelivered to the heart chambers in a sequence that causes the heartchambers to contract in synchrony, increasing the pumping power of theheart and delivering more blood to the peripheral tissues of the body.In the case of dysynchrony of right and left ventricular contractions, abiventricular pacing therapy may pace one or both ventricles. Bi-atrialpacing or pacing of all four heart chambers may alternatively be used.

SUMMARY

Example 1 is a system for facilitating placement of a lead in or on apatient's heart includes a first lead apparatus, a second leadapparatus, a user interface, and a processor. The first lead apparatusis configured for positioning a reference sensor element at a rightheart location, the right heart location in either the right atrium orright ventricle. The second lead apparatus is configured to advance acardiac electrode to a left heart site of the patient's heart. Thesecond lead apparatus includes at least one lead apparatus sensorelement. The processor is coupled to the user interface, the referencesensor element, and the lead apparatus sensor element. The processor isconfigured to measure, using signals produced by the reference and leadapparatus sensor elements, a distance parameter indicative of a distancebetween the reference sensor element at the right heart location and theat least one lead apparatus sensor element at each of a plurality ofleft heart locations in either the left ventricle or a coronary venouspathway, determine a separation distance for each of the plurality ofleft heart locations from the right heart location based on the distanceparameter measurements, and determine that the separation distance for alocation of the plurality of left heart locations from the right heartlocation is less than a threshold distance based on the separationdistance for the location. The threshold distance representative ofunsuitability for pacing, the processor configured to cause theinterface to produce a physician perceivable output indicating theunsuitability for pacing at the location.

In Example 2, the system of Example 1, wherein the first and second leadapparatuses respectfully comprise a cardiac electrical lead having oneor more electrodes configured for electrical stimulation of cardiactissue.

In Example 3, the system of Example 1, wherein the first lead apparatuscomprises a catheter, and the second lead apparatus comprises a cardiacelectrical lead having one or more electrodes configured for electricalstimulation of cardiac tissue.

In Example 4, the system of any of Examples 1-3, wherein the referencesensor element and the apparatus sensor element respectively comprise anultrasonic sensor.

In Example 5, the system of any of Examples 1-3, wherein the referencesensor element and the apparatus sensor element respectively comprise apiezoelectric sensor, a piezoresistive sensor, a strain sensor, anaccelerometer, an optical displacement sensor, or a deformation sensor.

In Example 6, the system of any of Examples 1-5, wherein the userinterface comprises a display, and the processor is configured todisplay an alert or warning indicating that the separation distance forthe location of the plurality of left heart locations from the rightheart location is less than the threshold distance for physician viewingon the display during lead placement.

In Example 7, the system of any of Examples 1-6, further including athird lead apparatus configured for positioning a second referencesensor element at a right heart location, wherein the right heartlocation is in right atrium if the first lead apparatus is in the rightventricle, or the right heart location is in the right ventricle if thefirst lead apparatus is in the right atrium, wherein the processor isfurther coupled to the second reference sensor element, the processorconfigured to determine a location of the second lead apparatus usingsignals produced by the reference sensor element, the second referencesensor element, and the at least one lead apparatus sensor element.

In Example 8, the system of claim 7, wherein the third lead apparatusfurther includes a third reference sensor element and the processor isfurther coupled to the third reference sensor element, wherein theprocessor is configured determine the location of the second leadapparatus using signals produced by the reference sensor element, thesecond reference sensor element, the third reference sensor element, andat least one lead apparatus sensor element.

In Example 9, the system of claim 8, wherein the processor is configuredto determine the location of the second lead apparatus by computing atime difference of arrival of a signal emitted from the at least onelead apparatus sensor element to each of the reference sensor element,the second reference sensor element, and the third reference sensorelement.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing various processes of a cardiac leadplacement method in accordance with embodiments of the presentinvention;

FIG. 2 is a flow diagram showing various processes of a cardiac leadplacement method in accordance with embodiments of the presentinvention;

FIG. 3 is a flow diagram showing various processes of a cardiac leadplacement method in accordance with embodiments of the presentinvention;

FIG. 4 shows various regions of a patient's heart on a heart map thatmay be used to facilitate cardiac lead placement in accordance withembodiments of the present invention;

FIG. 5 is a table of electrical and mechanical characteristics that maybe used to identify ischemic and myocardial infarction (MI) affectedmyocardium, viable myocardium, and a border region between ischemic/MIaffected and viable myocardium to facilitate cardiac lead placement inaccordance with embodiments of the present invention;

FIG. 6 is an illustration of a patient's heart and a lead placementapparatus implemented in accordance with embodiments of the presentinvention;

FIGS. 7 and 8 are tables that may be used to store and/or displayinformation that may be useful to the physician during a lead placementprocedure in accordance with embodiments of the present invention;

FIGS. 9A-10B show strain maps or portions thereof that may be developedin accordance with embodiments of the present invention and presented tothe physician to aid in lead placement;

FIG. 11 is a plot of ventricular tissue strain measured during a cardiaccycle using a distance-based measuring technique in accordance withembodiments of the present invention; and

FIG. 12 illustrates a system for facilitating lead placement inaccordance with embodiments of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration, various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

Systems, devices or methods according to the present invention mayinclude one or more of the features, structures, methods, orcombinations thereof described hereinbelow. For example, a device orsystem may be implemented to include one or more of the advantageousfeatures and/or processes described below. It is intended that suchdevice or system need not include all of the features described herein,but may be implemented to include selected features that provide foruseful structures and/or functionality. Such a device, system ormethodology may be implemented to provide a variety of therapeutic ordiagnostic functions.

Embodiments of the invention are directed to systems and methods forassisting physicians during lead placement and electrode implantation.Aspects of the invention are directed to evaluating cardiac tissue, suchas candidate pacing sites, using multiple sensors situated on one ormore leads, on one or more lead placement apparatuses, or on both a leadand a lead placement apparatus. Various embodiments of the inventionemploy a multiplicity of spatially distributed sensors configured tosense cardiac mechanical motion.

Suitable sensors include ultrasonic sensors, piezoelectric sensors,piezoresistive sensors, strain sensors, accelerometers, and opticaldisplacement or deformation sensors, among others. Various measurementsare made using the multiplicity of spatially distributed sensors, suchas distance between sensors measurements, measurements derived fromdistance data, local and/or global strain measurements, mechanical delaymeasurements, and electro-mechanical delay measurements. In the case ofultrasonic sensors, distance measurements and/or strain measurementsderived from distance measurements are preferably made using asonometric measuring technique. Suitable sonometric distance measuringtechniques and distance sensing arrangements are disclosed in U.S. Pat.Nos. 7,233,821 and 6,795,732, which are incorporated herein byreference. Results of distance measurements and/or strain or stressmeasurements derived from distance measurements are preferably presentedto a physician for purposes of guiding lead placement, such as byindicating suitability of cardiac tissue locations as potential pacingsites. These results may be presented in various forms, such as one ormore of data, text, indicia, graphics, imaging or other forms.

According to various embodiments, methods are directed to guidingcardiac lead placement using displacement sensors situated on thecardiac lead and/or the lead placement apparatus. Displacementinformation developed from the displacement sensors may be used toestimate distance of one sensor relative to another sensor, from whichan estimate of anatomical location of the cardiac lead may be made asthe lead is advanced by the physician. The displacement information maybe used to derive other distance-based parameters, such as strain orvelocity. Mechanical information derived from the displacement sensorsmay be used to determine mechanical delay characteristics of cardiactissue, which may be combined with electrical activity information toprovide electro-mechanical delay information for physician use. With theelectrical delay information and mechanical delay information derivedfrom analysis of distance data, a lead/pacing pole may be guided to theregion with larger mechanical and/or electromechanical delay.

According to various embodiments, one or more distance sensors may besituated close to the distal tips of one or more leads and/or leadplacement apparatuses. One or more distance sensors may be distributedalong the lead body or along a sheath of a lead placement apparatus.Distance and/or a derivative parameter of distance between the lead(s)and/or lead placement apparatus(es), and thus candidate pacing sites,may be continuously monitored. Candidate pacing sites may be evaluatedon the basis of one or more of separation distance (e.g., maximumseparation distance), stress or strain (e.g., regions of maximum oruniform strain or stress), mechanical delay, electrical delay, andelectro-mechanical delay.

Based on patient needs, the distance-based information may be used bythe physician to select a suitable pacing site and to guide a cardiaclead/electrode to the selected pacing site. An imaging tool, such asechocardiography, may also be implemented into the system to provideautomated feedback regarding the performance of the heart, optimizingpacing site selection, and pacing parameters. Influence of breathing mayalso be removed by a pre-set filter or by averaging a certain n numberof beats. Reducing, minimizing or eliminating the influence of breathingis often necessary as the distance and strain/stress measure mightchange depending on which phase of the respiratory cycle it was measuredfrom.

Turning now to the figures, FIG. 1 is a flow diagram showing variousprocesses of a cardiac lead placement method in accordance withembodiments of the present invention. According to the embodiment shownin FIG. 1, a reference sensor is positioned 10 at a first location of apatient's heart. A second sensor is moved 12 along the heart atlocations spatially separate from the first reference sensor.Preferably, the second sensor is moved to a multiplicity of discretesecond locations of the heart for purposes of making one or moremeasurements, it being understood that such measurements may be madewhile the second sensor is continuously moved. Distance data isgenerated 14 for each of the discrete second locations of the heart. Thedistance data may include a measurement of separation distance betweenthe first and second sensors and/or a measurement that can be derivedfrom separation distance information.

Strain or stress estimates are determined 16 for the discrete secondlocations of the heart derived from the distance parameters. Accordingto embodiments, an output is generated 18 indicative of one or more ofthe distance data measurements, strain estimates, and stress estimates.The output is preferably of a type that is useful to the physician forassessing structural, mechanical, electrical, and/orelectrical-mechanical characteristics of the patient's heart. Forexample, the output is preferably of a type that is useful to thephysician for assessing suitability of the multiplicity of secondlocations as pacing sites.

According to various embodiments, one or more sensors may be situated ona right ventricular lead, lead delivery apparatus or catheter andpositioned at the apical region. One or more sensors may be situated ona left ventricular lead, lead delivery apparatus or catheter and movedalong the left ventricle (or vice-versa). A right atrial lead, leaddelivery apparatus or catheter may support one or more sensors and bepositioned in the right atrium to serve as a reference foratrial-to-ventricle electrical or mechanical delay measurements. The canor housing of an implantable medical device, such as a cardiac rhythmmanagement system or implantable cardioverter/defibrillator, may itselfbe used as a reference by inclusion of an appropriate sensor.

Embodiments of the present are directed to an acute methodology ofmaking distance measurements using a multiplicity of implantablesensors, in which at least one of the sensors is removed from thepatient's body upon completion of the medical procedure (e.g., leaddelivery/placement procedure). Acute methodologies of the presentinvention are directed to enhancing physician evaluation of candidatepacing sites during a lead placement procedure. According to suchembodiments, one or more sensors are typically disposed on a catheter(e.g., sensor catheter or lead delivery catheter) and positioned at alocation within the right atrium or right ventricle, for example. Oncepositioned, the right heart sensor(s) may be used as a positionalreference, by virtue of being situated at a relatively fixed positionwithin the heart.

A lead or lead delivery catheter may be provided with one or moresensors. The lead/lead delivery catheter may be configured for leftheart access, such as epicardial access or transvenous (via the coronarysinus and coronary venous pathway, for example). The lead/lead deliverycatheter is advanced along the left heart tissue and variousdistance-based measurements are taken, preferably at discrete left heartlocations, using sensor data produced by the spatially distributedsensors at right and left heart positions. Distance-based measurementdata is preferably communicated to the physician performing the leadplacement procedure. As discussed above, the distance-based measurementdata is preferably of a type that is useful to the physician forassessing structural, mechanical, electrical, and/orelectrical-mechanical characteristics of the patient's heart, such asfor assessing suitability of discrete left heart locations as pacingsites.

Obtaining distance-based measurements in accordance with the presentinvention is particularly useful when delivering left heart leads forheart failure patients. It is theorized that a heart failure patient'sresponse to cardiac resynchronization therapy is enhanced when pacingelectrodes are widely separated, so that a large volume of ventriculartissue interposes the pacing electrodes. For example, to promote bettersynchronization between the right and left ventricles, it may bebeneficial to place the RV and LV electrodes relatively far apart.

Distance-based measurements obtained in accordance with the presentinvention provides the physician with lead/electrode separationdistances during lead placement, so that the RV and LV electrodes can beimplanted with an appropriate separation distance therebetween. Forexample, a discrete left heart location that provides a maximumseparation distance relative to a right heart reference sensor locationmay be selected as a desired (e.g., optimal) location for implanting anLV electrode. The physiologic basis for spacing the RV and LV electrodeswidely, rather than closely, is discussed, for example, in RadiographicLeft Ventricular-Right Ventricular Interlead Distance Predicts the AcuteHemodynamic Response to Cardiac Resynchronization Therapy, The AmericanJournal of Cardiology, Volume 96, Issue 5, 1 Sep. 2005, Pages 685-690).

By way of further example, incremental distance-based measurements maybe made using left and right heart sensors. The distance-basedmeasurements may be used to derive strain or stress measurements, suchas by using distance curves developed using distance measurements.Distance curves may be used to provide an estimate of cardiac tissuestress or strain throughout the cardiac cycle, such as in the mannerdiscussed in Ventricular Preexcitation Modulates Strain and AttenuatesCardiac Remodeling in a Swine Model of Myocardial Infarction, Shuros etal, Circulation. 2007 116.

It is theorized that a heart failure patient's response to cardiacresynchronization therapy is enhanced when pacing electrodes at or nearventricular tissue that is under greater (or greatest) strain or stressrelative to other regions of the ventricle. Strain or stressmeasurements derived from distance measurements obtained in accordancewith the present invention provides the physician with a mapping ofcardiac tissue stress or strain, so that the LV electrode(s) can beimplanted at or near those regions of greater or greatest strain/stressfor purposes of unloading these regions. The LV electrode(s) mayalternatively, or in addition, be positioned at a region or regions thatprovide the most uniform stress or strain distribution.

FIG. 2 is a flow diagram showing various processes of a cardiac leadplacement method in accordance with embodiments of the presentinvention. According to the embodiment shown in FIG. 2, a referencesensor is positioned 20 at a right heart location of a patient's heart.A cardiac lead apparatus is provided that supports at least one leadapparatus sensor. The lead apparatus may be a medical electrical lead, alead delivery catheter or sheath, or a combined lead/lead deliveryapparatus. The lead apparatus is advanced 22 to a multiplicity of leftheart locations. A distance parameter is measured 24 for each of theleft heart locations, the distance parameter indicative of a distancebetween the reference sensor and the lead apparatus sensor.

Strain or stress estimates are preferably determined 26 for the leftheart locations derived from the distance parameters. A physicianperceivable output developed from one or more of the measured distanceparameters, strain estimates, and stress estimates is produced 28. Forexample, the physician perceivable output may indicate the suitabilityof the left heart locations as pacing sites. By way of further example,the physician perceivable output may include an alert or warningindication that the spacing between right and left heart electrodes istoo small (e.g., separation distance <1 cm or <2 cm) or that the regionis of lower strain/stress relative to other regions, and that thispacing site should not be considered a good candidate pacing siterelative to others.

FIG. 3 is a flow diagram showing various processes of a cardiac leadplacement method in accordance with embodiments of the presentinvention. According to the embodiment shown in FIG. 3, a reference leador lead delivery apparatus that supports one or more sensors ispositioned 30 at a desired location. The desired location may be in theright ventricle or right atrium of a patient's heart. An LV lead or leaddelivery apparatus that supports one or more lead apparatus sensors ismoved 32 to a multiplicity of discrete left heart locations. A distanceparameter is measured 34 to provide an estimate of separation distancebetween the reference and lead apparatus sensors for each of the leftheart locations, thereby providing a measure of separation distancebetween the lead tips or pacing poles. As is shown in FIG. 3, strain orstress data may be computed 36 based on the distance estimates.Alternatively, or in addition, mechanical and/or electro-mechanicaldelay data may be determined 38 using the distance estimates and, in thecase of electro-mechanical delay data, electrical activity data acquiredfrom the electrode(s) of the leads/lead delivery apparatuses (which mayinclude use of a can or indifferent electrode).

It may be desirable to provide the physician with an estimate of theanatomical location 40 of the LV lead or lead delivery apparatus in oron the left ventricle during lead placement. FIG. 4 shows variousregions of the heart 50 on a heart map. The left ventricular regions maybe classified according to nine regions in the manner shown in FIG. 4.Other ways to classify the ventricular regions of interest arecontemplated. Depending on the distance measured between the referencesensor (e.g., RV or RA sensor) and the LV lead/lead delivery apparatussensor, the position of the LV lead/lead delivery apparatus may be shownon a map of the left ventricle, such as that shown in FIG. 4.

The heart maps may be generated in real-time during the placement andimplant procedure. The range of distances may be decided based onsimilar heart size population. Knowing the approximate location of thereference sensor, separation distance between the reference sensor andthe LV lead/lead delivery apparatus sensor, and using a heart mapappropriate for the particular patient, the approximate anatomicallocation of the LV lead/lead delivery apparatus may be determined. Theanatomical location information may be communicated to the physician inreal-time to facilitate lead placement.

From the continuous measure of distance between the multiplicity ofspatially distributed sensors, a guide about where the lead(s) is on theventricular wall can be determined. A population-based(heart/ventricular-size based) estimate of distances from the RV apicallead tip to the LV regions, for example, can be obtained and used toguide or map the location of the LV lead. The different LV locations maybe relatively simple as shown in FIG. 4. Maps for specific RV and/or LVlocations and with better resolution can be generated for enhancedguidance. If the anatomical position of where the lead needs to beplaced is decided or estimated, then the map may be used to identify ifthe lead is close to the region of interest.

As a lead is advanced further through the different regions of the heartor just prior to deciding on the optimal lead location, the region maybe evaluated 42 to ensure that it is not an ischemic or myocardialinfarction (MI) affected region. This evaluation 42 may be performedusing known imaging techniques. Alternatively, or in addition, capturevoltage levels may evaluated to determine if large voltage changesresult from capture testing at a given region. A significant increase involtage needed to effect capture may signify ischemic/MI affectedmyocardium.

Another approach to evaluating a region of the heart to determinepresence of ischemic/MI affected myocardium involves charting electricaland mechanical characteristics or morphology of the region. FIG. 5 is atable that may be used in such an evaluation. The table shown in FIG. 5may be used to identify ischemic/MI affected myocardium, viablemyocardium, and a border region between ischemic/MI affected and viablemyocardium. For example, a region of ventricular tissue may be evaluatedusing techniques of the present invention, from which electrical andmechanical characteristics may be derived.

As shown in FIG. 5, observable changes in both electrical and mechanicalcharacteristics occur when moving the lead/lead delivery apparatus fromviable myocardium to ischemic/MI affected myocardium (a change in signin FIG. 5 from negative to positive or vice-versa). Moving the lead/leaddelivery apparatus from ischemic/MI affected myocardium to borderingtissue generally results in an observable change in electrical, but notmechanical, characteristics. Hence, it may be desirable to obtain bothmechanical and electrical measurements in accordance with certainembodiments, when avoiding ischemic/MI affected myocardium during a leadplacement procedure is of heightened importance.

It is understood that other methodologies for detecting ischemic/MIaffected myocardium may be employed, alternatively or in addition tothose discussed above. According to one lead placement approach, forexample, prior to final lead implantation, an ischemic/MI affectedmyocardium location algorithm may be automatically triggered to ensurethat the lead is not placed in an ischemic or infarct region.

FIG. 6 is an illustration of a patient's heart 50 and a lead placementapparatus implemented in accordance with embodiments of the presentinvention. FIG. 6 shows a right heart lead apparatus 52 placed withinthe right atrium. A right heart lead apparatus 54 is shown placed in theright ventricle. A left heart lead apparatus 56 is shown in FIG. 6 ashaving been moved to three discrete left heart positions (positions 1,2, and 3, ranging between apical, mid, and basal locations of the leftventricle). The term lead apparatus is intended to refer to varioustypes of apparatuses, including, but not limited to, leads, leaddelivery apparatuses, catheters, sheaths, and probes, for example.

As was previously discussed, the right heart lead apparatus ispreferably situated at a right heart location so that its sensor(s) maybe used as a relatively fixed reference. In general, a single rightheart lead apparatus (ventricular or atrial) is employed,notwithstanding that FIG. 6 shows tandem lead apparatuses (RA and RV) inthe right heart. In some embodiments, it may be advantageous to deployRV and RA lead apparatuses each having a reference sensor or a single RVor RA lead apparatus having a multiplicity of spaced-apart sensors. Sucha configuration of spatially distributed sensors affords the opportunityto use locating techniques akin to triangulation for accuratelydetermining the location of the LV lead apparatus, discretely orcontinuously.

For example, multilateration, also known as hyperbolic positioning, maybe used to locate the LV lead apparatus 56 by computing the timedifference of arrival (TDOA) of a signal emitted from the LV leadapparatus sensor to three or more receiving sensors disposed on one orboth of the RV and RA lead apparatuses. A variation of this approach maybe used, by which the LV lead apparatus sensor receives a synchronizedsignal transmitted from three or more spatially separated sensorsdisposed on one or both of the RV and RA lead apparatuses. In thisconfiguration, the location of the LV lead apparatus sensor may bedetermined by measuring the TDOA of the synchronized signals transmittedfrom the spatially separated sensors disposed on one or both of the RVand RA lead apparatuses.

Trilateration is another method that may be used to determine thelocation of the LV lead apparatus sensor relative to two or morespatially separated sensors disposed on one or both of the RV and RAlead apparatuses. Trilateration uses the relative fixed (i.e., known)locations of two or more right heart reference sensors, and the measureddistance between the LV lead apparatus sensor and each reference sensor.Algorithms for implementing a multilateration and trilaterationmeasuring methodology are well known to those skilled in the art.

FIGS. 7 and 8 are tables that may be used to store and/or displayinformation that may be useful to the physician during a lead placementprocedure. FIG. 7 provides distance measurement information, while FIG.8 provides mechanical timing measurement information. Although notshown, a similar table may be used to provide electrical timing or delaymeasurement information. FIG. 7 tabulates separation distances betweenthe LV lead apparatus 56 relative to various reference or anchor sensorsof the RV lead apparatus 54, RA lead apparatus 52, and other referencesensors that may be deployed at each of the discrete LV positions (e.g.,positions 1 and 2) shown in FIG. 6.

FIG. 8 shows various mechanical and timing characteristics for each ofthe discrete LV positions shown in FIG. 6. These characteristics includelocal maximum strain, time to peak displacement, and other mechanicaltiming characteristic that may be of interest. As previously discussed,electrical activity and timing data may be similarly tabulated andpresented to the physician. These data may be presented in real-time ina manner useful to the physician during lead placement. Moreover, thesedata (and data derived from these data) may be combined to provideadditional useful information, such as electro-mechanical delay data.

FIGS. 9A-10B show strain maps or portions thereof that may be developedin accordance with embodiments of the present invention and presented tothe physician to aid in lead placement. The strain maps of FIGS. 9A-10demonstrate that local strain information may be derived from distancemeasurements made using distance sensors of the present invention (e.g.,ultrasonic microcrystal sensors). FIGS. 9A and 9B show circumferentialand longitudinal strain maps, respectively, that may be derived using adistance measuring technique of the present invention. It is noted thatthe strain estimation methodology is the same for the two maps. Thearrangement of the sensors, however, is different. In the case ofultrasonic microcrystal sensors, the sensor crystals are oriented alongthe length of the heart (from base to apex) to obtain longitudinalstrain and along the circumference of the heart to obtaincircumferential strain. The lead or sensor arrangement may be placed ineither orientation to obtain similar strain maps to identify thestrained regions.

FIGS. 10A and 10B are exploded views of longitudinal and circumferentialstrain map information for RV, septal, and LV regions of the leftventricle. The maps may be used to facilitate a visual understanding ofthe stress profile of a given region of the heart, such as byhighlighting regions of high/maximum stress or uniform stress.

FIG. 11 is a plot of ventricular tissue strain measured during a cardiaccycle using a distance-based measuring technique in accordance with thepresent invention. The strain signal is shown in time-alignment with anECG signal, a left ventricular pressure signal, and an aortic flowsignal. In particular, FIG. 11 shows each of these signals for anintrinsic and a paced beat (intrinsic and paced strain signals 60 and61; ECG intrinsic and paced signals 70 and 71; intrinsic and paced LVpressure signals 80 and 81; and intrinsic and paced aortic flow signals90 and 91). The plot of FIG. 11 may be used by the physician to evaluateall portions of the cardiac cycle in terms of strain or stress.

It is theorized that a region of ventricular tissue that experiencesgreatest strain or strain rate during a cardiac cycle is also the regionassociated with the largest electrical delay. The strain/ECG profile ofFIG. 11 allows the physician to visually evaluate and identify highlystressed regions as candidate pacing sites, such as a locationassociated with a peak systolic strain rate 62 shown in FIG. 11. Somestudies have suggested that the strain rate during isovolumetriccontraction is of particular interest, while other studies havesuggested that strain rate during the ejection phase is of particularinterest. The strain/ECG profile of FIG. 11 allows the physicianevaluate stressed regions as candidate pacing sites for each of thesephases. For example, the strain curves and the ECG can be used todetermine peak strain during a particular period of interest, such assystolic phase, ejection phase, etc., any of which may be used based onphysician preference. Electro-mechanical timing information can also beobtained from such a set up.

FIG. 12 illustrates a system for facilitating lead placement inaccordance with embodiments of the present invention. The system 100shown in FIG. 12 includes a first lead apparatus 102 and a second leadapparatus 104. Each of the lead apparatuses 102, 104 supports one ormore sensors 105, 109 configured to facilitate distance measurements inmanners discussed hereinabove. Although the lead apparatuses 102, 104are each shown to support several sensors 105, 109, it is understoodthat one or both of the lead apparatuses 102, 104 may support only asingle sensor 105, 109. As previously discussed, the sensors 105, 109 beconfigured as ultrasonic sensors (e.g., ultrasonic microcrystalsensors), piezoelectric sensors, piezoresistive sensors, strain sensors,accelerometers, optical displacement or deformation sensors, amongothers. The lead apparatuses 102, 104 may be configured to include oneor more electrodes 103, 107.

The lead apparatuses 102, 104 are coupled to a processor 106, typicallyby electrical or optical conductors 112, 114 that extend from theproximal end of the lead apparatuses 102, 104. The processor 106 iscoupled to a user interface 108, which typically includes a display 110and a user input device 111. The processor 106 is configured toimplement the algorithms and methods discussed previously to facilitatelead placement. The system shown in FIG. 12 may be implemented tofacilitate lead placement in manners described hereinabove and inaccordance with embodiments of the present invention.

Various modifications and additions can be made to the preferredembodiments discussed hereinabove without departing from the scope ofthe present invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

We claim:
 1. A system for facilitating placement of a lead in or on apatient's heart, comprising: a first lead apparatus configured forpositioning a reference sensor element at a right heart location, theright heart location in either the right atrium or right ventricle; asecond lead apparatus configured to advance a cardiac electrode to aleft heart site of the patient's heart, the second lead apparatuscomprising at least one lead apparatus sensor element; a user interface;and a processor coupled to the user interface, the reference sensorelement, and the lead apparatus sensor element, the processor configuredto measure, using signals produced by the reference and lead apparatussensor elements, a distance parameter indicative of a distance betweenthe reference sensor element at the right heart location and the atleast one lead apparatus sensor element at each of a plurality of leftheart locations in either the left ventricle or a coronary venouspathway, determine a separation distance for each of the plurality ofleft heart locations from the right heart location based on the distanceparameter measurements, and determine that the separation distance for alocation of the plurality of left heart locations from the right heartlocation is less than a threshold distance based on the separationdistance for the location, the threshold distance representative ofunsuitability for pacing, the processor configured to cause theinterface to produce a physician perceivable output indicating theunsuitability for pacing at the location.
 2. The system of claim 1,wherein the first and second lead apparatuses respectfully comprise acardiac electrical lead having one or more electrodes configured forelectrical stimulation of cardiac tissue.
 3. The system of claim 1,wherein the first lead apparatus comprises a catheter, and the secondlead apparatus comprises a cardiac electrical lead having one or moreelectrodes configured for electrical stimulation of cardiac tissue. 4.The system of claim 1, wherein the reference sensor element and theapparatus sensor element respectively comprise an ultrasonic sensor. 5.The system of claim 1, wherein the reference sensor element and theapparatus sensor element respectively comprise a piezoelectric sensor, apiezoresistive sensor, a strain sensor, an accelerometer, an opticaldisplacement sensor, or a deformation sensor.
 6. The system of claim 1,wherein the user interface comprises a display, and the processor isconfigured to display an alert or warning indicating that the separationdistance for the location of the plurality of left heart locations fromthe right heart location is less than the threshold distance forphysician viewing on the display during lead placement.
 7. The system ofclaim 1, further including a third lead apparatus configured forpositioning a second reference sensor element at a right heart location,wherein the right heart location is in right atrium if the first leadapparatus is in the right ventricle, or the right heart location is inthe right ventricle if the first lead apparatus is in the right atrium,wherein the processor is further coupled to the second reference sensorelement, the processor configured to determine a location of the secondlead apparatus using signals produced by the reference sensor element,the second reference sensor element, and the at least one lead apparatussensor element.
 8. The system of claim 7, wherein the third leadapparatus further includes a third reference sensor element and theprocessor is further coupled to the third reference sensor element,wherein the processor is configured determine the location of the secondlead apparatus using signals produced by the reference sensor element,the second reference sensor element, the third reference sensor element,and at least one lead apparatus sensor element.
 9. The system of claim8, wherein the processor is configured to determine the location of thesecond lead apparatus by computing a time difference of arrival of asignal emitted from the at least one lead apparatus sensor element toeach of the reference sensor element, the second reference sensorelement, and the third reference sensor element.